The following United States patents represent the closest known prior art, U.S. Pat. Nos.: 3,076,431; 3,158,133; 3,158,134; 3,205,857; 3,297,020; 3,844,273; 3,948,249; 4,239,018; 4,247,758.
Since the advent of artificial insemination techniques, it has been possible to breed cattle to optimize characteristics such as size, milk productivity, disease resistance, and the like. However, although artificial insemination no longer requires the presence of the breeding bull at the time of insemination, it still requires that the farmer or rancher determine the exact time of estrus of a cow, so that the insemination will fertilize the cow. The accurate detection estrus, or standing heat in cattle, is a problem long recognized but unsolved in the prior art.
A cow comes into heat approximately every 21 days, and then remains in heat for approximately 10 to 12 hours. The cow then ovulates approximately 14 hours after going out of heat. The time of ovulation is the optimum time for artificial insemination. If insemination is successful, the cow will be pregnant for 280 days. After calving, the ideal situation from the farmers standpoint is to reimpregnate the cow within 45 to 60 days after calving.
However, if it is not known when the cow first entered heat, the timing of the artificial insemination must be approximate, and a significant number of inseminations will fail to produce pregnancy. The farmer must then wait for the next estrus period to again attempt insemination. It is reliably estimated that it cost a dairyman three dollars per day per cow if the cow is not pregnant when it could be pregnant. In an average size dairy herd of 400 cows, with an average calving interval of 14 months, accurate determination of standing heat could lower the calving interval to an average of 11.5 months. This savings of 45 days in the pregnancy cycle, multiplied by three dollars per day and by 400 cattle, can result in a net savings of $54,000 per year. Thus it is clear that the accurate determination of estrus onset in cattle is extremely important to dairymen, as well as other cattle breeders.
One type of device known in the prior art for detecting standing heat employs a dye or dye forming chemicals disposed in a frangible pack and secured to the base of the tail of each cow in a herd. With the onset of estrus in any cow, the other cows will try to mount the one in heat, breaking the frangible pack and spreading the dye over the animal sufficiently to warn the cattleman that the cow has entered heat. However, if several cows enter heat on the same day, or if precipitation should wash away the dye, it is difficult to determine which cow is in heat. Furthermore, it cannot be determined to within 12-24 hours when estrus has begun, so that the timing of insemination involves too much guesswork and not enough certainty.
Another approach known in the prior art employs a temperature sensor placed in the vagina of the cow, and includes a radio transmitter which emits a signal when the internal temperature rises. This temperature gain may indicate onset of estrus, or may also indicate a fever due to bovine illness. Also, experience has shown that many of these devices are lost by being expelled during urination by the cow.
Other prior art attempts to detect estrus involve a radio transmitter strapped to the leg of each cow and coupled to a pedometer. The theory is that a cow entering heat will be more restless and will take more steps per day than a cow not in heat. The radio transmitter will emit a signal indicative of the number of steps and apprise the rancher each day. However, other factors may determine the number of steps per day, such as changes in grazing habits, the presence of other animals or humans, and the like.
A significant failing of all of these methods and apparatus, in addition to the shortcomings noted already, is that they do not determine the exact time of onset of estrus, and thus cannot provide the cattle owner with accurate information for optimal timing of the artificial insemination.